Which expert can talk about the essential difference between frying and roasting, taste and water loss?

Cooking fruits and vegetables with hot air in the oven will be slower for several reasons. First of all, compared with water and oil, the density of air is lower, so air molecules will not collide with food so frequently, and it takes a long time for energy to be transmitted to food. Secondly, when a low-temperature object is put into a high-temperature oven, a layer of "interface" between air and water molecules is generated on the surface, which further reduces the collision frequency. Adding a convection fan can accelerate the air circulation, destroy the interface layer and improve the cooking speed. Finally, in dry air, the moisture of food will evaporate from the surface, so most of the external energy is absorbed, and only a small amount of energy can reach the core. Therefore, the efficiency of baking method is much lower than that of frying method.

Of course, it is precisely because the heat transfer medium inside the oven is quite thin that it is very suitable for drying food, and the food crystals can be baked into a semi-dry state (for example, tomatoes are baked with water to improve the flavor concentration); You can also bake food almost completely for storage, or bake it hard or crisp. Once the surface is dry, the temperature of the food will rise to near the temperature of the oven. At this time, carbohydrates and the quality of eggs themselves will brown, producing hundreds of brand-new taste molecules and aromatic molecules, thus emitting a stronger flavor.

Vegetables are often oiled before baking, so simple pretreatment will bring two important results. A thin layer of oil on the surface will not evaporate like the water in food, so the oil will be used to raise the temperature of itself and food after absorbing the heat of oven air, so the surface temperature of food will be higher than that without oil, and food can also turn golden yellow or be completely cooked. Secondly, some oil molecules will participate in the browning reaction, change the composition of the reaction products, and emit a stronger unique flavor.

deep-fry

Baked vegetables coated with oil are sometimes called "frying". frying or frying with oil can really dry the surface of food and turn it into golden yellow, and make the flavor of oil itself more distinctive. At this time, the ingredients can be partially soaked in oil (fried), completely soaked in oil (fried), or just evenly soaked in thin oil (fried); The oil temperature is usually between 160℃ and 190℃. Real frying is faster than roasting, because the density of oil is much higher than that of air, so high-energy oil molecules collide with food more frequently. The key to the success of the frying method is that the size of the ingredients and the cooking temperature should be appropriate, so that when the surface is beautiful golden yellow, the inside is already cooked. Starch vegetables are the most common fried plant foods, and important examples of potatoes will be discussed in the second chapter. Many delicate vegetables or fruits can do this: first, wrap a layer of paste or bread crumbs on the surface, which will become crisp and brown, and isolate the ingredients inside from direct contact with high temperature.